The invention relates to a belt coil as transmitter/receiver antenna in a transponder apparatus in human and veterinary medical apparatus.
For the recording of measuring data of medically interesting physiological parameters such as pressure, temperature, pH values etc, in connection with humans or animals, it is often important to gather these data over an extended period and as much as possible under normal living conditions, for example, in connection with a long time EKG. This is done so far in a way which is not satisfactory as far as the measuring technique is concerned particularly if the measurement values have to be derived from deeply within the body and cannot be derived directly from signals available at the skin surface, such as bladder pressure or brain pressure. In order to permit taking the measurements as much as possible under normal living conditions, the measuring equipment must not negatively affect the physiological functions and the comfort of the patient. The measuring equipment should therefore be such that it can be carried directly on the body or even be arranged within the body and it should be easy to service.
The biggest problem with such devices concerns the provisions for supplying the required operating energy. Inspite of substantial progress in minimizing the energy consumption of integrated circuits, even the most energy efficient microchips do not permit longtime measurements over periods of more than a few days or possibly weeks. Then the battery or accumulator of the measuring apparatus must be replaced. Because of the short servicing cycles such devices are not suitable for implantation in some depth within a body since each battery change would require a surgical procedure.
If, today, measuring data from deep within a human or animal body have to be collected over extended periods, the following procedure is employed:
The actual measuring value sensor is implanted into the body at the location where the value of interest is to be taken. The measurement value obtained by the sensor is then transmitted electrically for example by way of a cable or mechanically by way of a pressure measuring catheter to a measurement data processing apparatus which is disposed outside the body or implanted into the body just below the skin.
There is a tendency to arrange the measurement data processing apparatus not outside the body, but to implant them increasingly below the skin. The high integration density of modern semiconductor chips permits the arrangement of complex functions on a small chip. As a result, the processing systems for many applications are sufficiently small so that they can be implanted subcutaneously.
However, also subcutaneously implanted measurement data processing apparatus must be supplied with energy. A servicing procedure for changing the battery is in that case substantially less objectionable to the patient since only a superficial disturbance in the skin is needed to access the apparatus. Since, however, also this procedure is not suitable for use over extended periods such as several months or years the technique of inductively in-coupling energy through the skin for the charging of batteries in the measuring system was introduced.
But although with the inductive charging no invasive procedures are needed for the charging of the battery, this solution still has some drawbacks. An important disadvantage of all equipment where the measurement value sensor and the processing electronics are spatially separated resides in the cable connection which has to extend through several tissue layers of the body in order to interconnect both. For example, for measuring the pressure in the bladder, the bladder wall must be penetrated by the pressure sensor catheter or by the electrical connection to the sensor element and a distance to the nearest skin surface which in this case is the belly cover, must be bridged. On one hand, in this way, the tissue areas are irreversibly damaged because of the formation of scars or by tissue changes around the penetration channel of the connection and, on the other hand, the cable connection is subjected to constantly varying stresses as a result of the unavoidable movement of the tissue. Over an extended period, this results in material fatique and fracture of the cable whereby the implant is placed out of service.
In the transponder technology, including passive transponders, the transponder apparatus is supplied with energy and the collected information is removed therefrom over a certain distance by a portable or stationary reading apparatus. To this end, the transponder apparatus includes a transmission/receiving antenna which must be brought so close to the transponder that it is within reach of the electromagnetic alternating field. These antennas are actually coils providing for a magnetic coupling. The antenna coils may have various configurations; rectangular or round frame coils, rod coils, flat conductor plate coils, etc. All these configurations have in common that they are rigid and include a predetermined number of conductor windings.
For the use in the measurement of physical values in the body, these coils are not suitable since they do not adapt to the various body shapes in particular body areas. If a magnetic field is to be established within the area of the belly, the coil must be worn around the belly. In that case, firm support must be provided for the coil so as to prevent its slipping out of position. However, the coil must still be flexible and expandable so that freedom of breathing and movement of the patient are not restricted. Furthermore, it must be easy to install and remove the coil. The coil structure must also be comfortable to wear, at least it should be soft and flexible. Such properties are not provided with the antenna coils presently available.
A portable transmission and read-out antenna for measuring values in connection with a living person has become known so far only in one case. This is a system for measuring the material stresses of a hip joint prosthesis. In this case, a passive transducer in the interior of the head of the prosthesis was used. The read-out antenna was attached around the thigh at the level of the groin. In this experiment, for mounting, the antenna was tightly attached around the quadriceps so that it remained in place. In addition, it was fixed to the thigh by an adhesive tape. The antenna was neither flexible nor could it be opened or closed.
With the further development of the transponder technology particularly passive transponders without their own energy supply, a possibility has become available to eliminate the problems of measuring the physical body values as mentioned above. Passive transponders receive the energy needed for their operation from an alternating magnetic field to which they are exposed. From this field, they generate, by magnetic induction, the electrical voltage needed for their operation. Also, the data transmission occurs with the passive utilization of the alternating magnetic field in that the data are modulated onto the magnetic field by imposition on the induction coil in the transponder. Highly integrated microchips today combine the sensor technology for recording and preprocessing the sensor values with the electronic components for the passive transducer into a single component. In this way, it is possible to implant the complete measuring apparatus at the location in the body where the measurements are to be taken. Servicing is no longer necessary. Such a passive transducer could remain implanted for as long as it can serve a purpose.
It is the object of the present invention to provide a magnetically sensitive transmission and receiving arrangement which can be placed onto a human or animal body whereby a passive transponder implanted into the body can be supplied with energy and to which the transponder can supply information also by way of the magnetic field of the magnetically sensitive transmission and receiving arrangement. At the same time, wearing the antenna should not limit the movements of the wearer or limit them only in a bearable manner.